Newbie E5061B user: please help me

Hi all, i'm currently studying the impedance behavior of some gold (or platinum) quartz crystals which frequency ranges from 5 to 10 MHz. In the past i used for this purpose an old HP 4192A but data acquisition was a lot complicated and the acquisition time for each scan was too low for my purposes. Accordingly, I have recently purchased an E5061B Network Analyzer with the following option (apart the hard disk): a) E5061B-3L5 LF-RF network analyzer with DC bias source, -1E5 high stability timebase and -005 impedance analysis. Unfortunately, I have some trouble looking about the measurement approach since some parameters here are quite different from those already used in the past with my old HP 4192A . As an example, I did some experiments using an example from the E5061B Network Analyzer Help (page 91, Gain-phase/Series-Through). While some parameters are obviously, some other for me not. Particularly,what I don't understand is the meaning of Avg, IF BW Auto, IFBW Auto limit? I see that these parameters in some way change the scan time as well as in some cases the frequency span and much probably the number of points which are acquisite with the experiment. Can someone help me about? Can someone suggest some reading about? many many thanks in advance Antonio

> Particularly,what I don't understand is the meaning of Avg, IF BW Auto, IFBW Auto limit? > I see that these parameters in some way change the scan time as well as in some cases the frequency span and much probably the number of points which are acquisite with the experiment. > > Can someone help me about? > Can someone suggest some reading about? > > many many thanks in advance > > Antonio

I don't know the E5061B, so the following is based on my experience using other VNAs, spectrum analyzers and lock-in amplifiers.

In simple terms

* Reducing the IF bandwidth * Increasing the average

both reduce the noise on the measurement.

If you use a smaller IF bandwidth, less noise is receiveed. Noise power will be proportional to IF bandwidth. You get a better dynamic range at reduced IF bandwidth.

However, the filters will have a settling time. That in general depends on many things (response, order etc), but is inversely proportiaal to the bandwidth. So the narrower the IIF bandwidth, the longer the filters take to settle, so the slower the sweep must be.

As the number of data points you look at increaseed, so more data points must be collected, the filter allowed to settle more times, so the sweep takes longer.

In my VNA at least (8720D) and I expect in a lot of VNAs, the frequency range is split into bands. It takes some time to switch between bands, so for the same number of data points, the same IF bandwidth, the sweep speed will not necessarily be the same.

To unashamedly copy what Dr_Joel wrote the other day, when averaging N data points, the method used is:

New_Data_Displayed=(New_Data/N)+Old_displayed_data*(N-1)/N

That performs an infinite impule response filter. It should be obvious that as you average more data the noise gets reduced. You also need to let the instrument settle for longer before taking readings off of the VNA.

For some measurements, where for example there is a lot of attenuation between the source and the receiver, you need to reduce noise and accept a longer measurement time. For other cases, this is not necesssary.

These issues of averaging, IF bandwidth and noise effects are fairly common to other instruments like the spectrum analyzer.

In general, the sweep speed is set automatically depending on the number of points and the IF bandwidth. You can generally override the defaults, but there is often not a lot of need to. One example I do know of where it needs to be done is in using long cables on some older VNAs. That is described in the application note +"10 Hints for Making Better Network Analyzer Measurements"+, Application Note 1291-1B. Also take a look at +"Understanding and Improving Network Analyzer Dynamic Range"

I'm doing impedance measurements with time since i'm interested how the quartz crystal properties changes with time so that i need to control or at least to know the scan time for each measurements .....

> I'm doing impedance measurements with time since i'm interested how the quartz crystal properties changes with time so that i need to control or at least to know the scan time for each measurements .....

Quartz is pretty damm stable. I'm not sure what changes you expect to see during the sweep time of a VNA. But at least on any VNA I have used, it is possible to control the sweep time.

You might want to consider subscribing to the +time-nuts+ mailing list.

http://leapsecond.com/time-nuts.htm

I suspect you would get a lot of useful advice about crystals.

Several of the subscribers to +time-nuts+ have multiple cesium oscillators. At least one (Tom Van Baak) has a hydrogen maser clock - which is more stable (and expensive!) than a cesium clock. Tom has taken cesium clocks up mountains for experiments to verify Einstein's theory of relativity.

There is a *lot* of expertese on the +time-nuts+ list about quartz oscillators.

Some of the more amuzing things on Tom's site are a really accurate wrist watch: